71 MPH but at a cost
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  1. #1
    PWCToday Regular Daveinpa's Avatar
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    71 MPH but at a cost

    Two big firsts from last weekend, The conditions were just right for high speed runs,
    the water was like glass, water temps in the low 70s and the air temps in the mid 70s
    On the first pass with my VE 920 X4 she ran 71 mph at 7710 rpm for the first time
    turning a Solas XII/ Mag C pump and 82mm exit nozzle with no issues.
    On the second longer pass of about 1/8 mile WOT run I got to experience the
    dreaded overstuffing pump tunnel phenomenon.
    It's something I don't what to do a second time, at 71 or + mph without warning
    I was tossed over the bars and beat across the water like a rag doll. It felt like being hit
    in the back from a runaway truck, I don't remember coming off the seat it happened
    so fast.
    When I finally stopped and open my eyes I did a body check and then though
    " What the hell was that "
    The ski was 20 foot away and still upright, I expected to see it in pieces, it wasn't,
    My neck and back took the beating, no broken bones
    Unfortunately I didn't have the Gopro on this ski, its was on my VE 970 X4, That
    was the ski I was really testing that day.
    I'd like to seen how crazy it looked and how it stuffed.
    The GPS is on the bottom so I don't know the top speed of the second run.

    So no more high speed runs until I find a fix, could be the 140mm C pump can't flow
    enough water when you back off the gas. I may swap out for my D pump but that
    one did not product the big speed numbers, Already looking at pump tunnel relief valves.
    I can rule out the grate because I wasn't running one.

    My preferred idea is do what Joe Portale did back in the 90s to one of his race skis
    that I have now, Its unique, they built up the keel line from bow to the tunnel by 1-2"
    He also added chines to either side of the build up
    The stock XP keel has a flat surface running up to the pump tunnel
    The ski rides like no other X4 Ive ever ridden. It rides high on the water, less drag,
    Its stable, hooks hard and 80% of the hull is out of the water when on plane, I think this
    would trap less water under the hull



  2. #2
    Top Dog JC-SuperJet's Avatar
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    Re: 71 MPH but at a cost

    Hopefully you didn't get a Concussion.

    Happens to Wake Boarders all the time, and they are falling at half the speed...

  3. #3
    PWCToday Regular Daveinpa's Avatar
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    Re: 71 MPH but at a cost

    My concern was a broken neck, With skis now running in the 90s and they have the same issue I'm not sure they would live to talk about it.

  4. #4
    PWCToday.com Is My Home Away From Home Matt Braley's Avatar
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    Re: 71 MPH but at a cost

    Wow. Congrats and I'm sorry about that spill. I thought I would be safe at 71 but now I'm thinking. The previous owner of my X4 said it happened to him at 74-75. Mine has the 155mm 951 plastic pump so maybe that is helping me. I have not been using mine as I should. Man I'm glad you are OK. Thank you for sharing.

  5. #5
    PWCToday Regular Daveinpa's Avatar
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    Re: 71 MPH but at a cost

    I think with that 155mm pump you should be good Matt, I never planned on this ski seeing more then 70 but you know how it goes, never fast enough.
    I'm going to concentrate on the 970 ski with the D pump from here on, its running just under 70 with a 16/23 at 8010, Needs a 17/24 or more

  6. #6
    Resident Guru 1983's Avatar
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    Re: 71 MPH but at a cost

    Glad you are ok
    Last edited by 1983; 09-19-2019 at 04:21 PM.

  7. #7
    PWCToday.com Is My Home Away From Home
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    Re: 71 MPH but at a cost

    The ZXI1100's had this issue on the first skis that came out in 1996. I think they drilled a couple relief holes in the pump shoe to mitigate it. Might be worth looking into the specifics.
    triceps are the biceps of the back of your arm.

  8. #8
    PWCToday.com Is My Home Away From Home Benflynn's Avatar
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    Re: 71 MPH but at a cost

    What's happening? Maybe an inverted thrust from the pump, but water doesn't compress, maybe cause water doesn't compress, I should of taken some fluid dynamics classes

  9. #9
    PWCToday.com Is My Home Away From Home Matt Braley's Avatar
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    Re: 71 MPH but at a cost

    Quote Originally Posted by Benflynn View Post
    What's happening? Maybe an inverted thrust from the pump, but water doesn't compress, maybe cause water doesn't compress, I should of taken some fluid dynamics classes
    It's a very common issue with conversion skis, drag skis, etc. I never thought it would be an issue for me but this thread makes me feel a little close for comfort. I want my skis to be very capable but I normally cruise around at 5 or 6 K rpm. Last weekend I did 94 miles with my 98SPX with a T tank in it.

    Dave your performance achievements with these things are through the roof! I've been thinking about this today. Over 70 with a 140mm pump is huge. Over 8K rpm is huge. Having the power to pull a Xll is really something as well. I'm very impressed.

  10. #10
    PWCToday.com Is My Home Away From Home Cliff's Avatar
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    Re: 71 MPH but at a cost

    Matt,

    What is a T tank and can you post pics of it? I am working with Chris at WCM on my ‘98 SPX build and extra fuel range would be nice in the X4.

    Thanks!

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